The present invention relates to a laser system for transferring energy to tissue during medical treatment procedures and, more particularly, to a system and method of measuring and controlling temperature of an optical fiber tip for the laser treatment system during operation.
It is well known that energy generators in the form of lasers have been utilized to treat many disease states, including cancer, tumors, and benign prostatic hyperplasia (BPH). During the course of such treatments, one parameter which has great importance is the temperature of the tissue being treated. For example, the current recommendation for forming lesions in the prostate as a treatment for BPH is to heat a small volume of tissue to 85xc2x0 C. for approximately three minutes. It will be appreciated that heating the tissue at a lesser temperature has the effect of incomplete lesion formation, while heating the tissue at a higher temperature can cause excessive tissue damage. Accordingly, the ability to accurately measure the temperature of the optical fiber tip during treatment, as well as control the power output of the laser to maintain the temperature at a desired level, is of primary concern.
It will be understood that there are several known ways of performing the temperature monitoring function for a laser system. One approach has been utilized in a laser treatment system known as the xe2x80x9cIndigo 830e Laseroptic Treatment Systemxe2x80x9d manufactured by Ethicon EndoSurgery, Inc. of Cincinnati, Ohio, which is also the assignee of the present invention. This approach involves relying upon the temperature dependence of the fluorescent response of a slug of material at the fiber tip to an optical stimulus. More specifically, a pulse of pump energy causes a fluorescence pulse in an alexandrite slug which is delayed by a time interval corresponding to a temperature of the material. By providing the stimulus signal in the form of a sinusoid, the response signal is likewise a sinusoid and the temperature is related to the phase shift or difference therebetween.
The signals which are compared in the 830e laser treatment system are the actual response or fluorescent signal from the alexandrite and a pair of timing signals (shifted 0xc2x0 and 90xc2x0 in phase) which are programmed in its electronics. In this way, digital timing signals are used to strip phase information from the response signal. It has been found, however, that several adjustments and calibrations are required under this approach due to the chain of amplifiers and filters involved. This not only adds complexity and cost to the set-up and maintenance of such systems, but creates an inherent variability between each laser treatment system that must be accommodated during manufacture and service.
Accordingly, it would be desirable for a system and method to be developed in which temperature of an optical fiber tip used with a laser device during treatment is able to be measured and controlled in a manner which minimizes the adjustments and calibrations required, improves the stability and repeatability between laser systems, and reduces complexity and cost.
In accordance with one aspect of the present invention, a method of sensing temperature at an optical fiber tip is disclosed as including the steps of positioning a slug of fluorescent material adjacent the optical fiber tip, providing an optical stimulus having a wavelength within a first predetermined range through at least one fiber optically linked to the optical fiber tip, wherein a desired optical fluorescent response having a wavelength within a second predetermined range from the fluorescent slug is generated, detecting a signal representative of the optical stimulus, detecting a signal representative of the optical fluorescent response, digitally processing the optical stimulus signal and the optical fluorescent response signal to determine a phase difference therebetween, and calculating a temperature for the optical fiber tip as a function of the phase difference. The phase difference between the optical stimulus signal and the optical fluorescent response signal may be determined directly or indirectly as a function of the phase difference between a reference signal and the optical stimulus signal and the phase difference between the reference signal and the optical fluorescent response signal.
In accordance with a second aspect of the present invention, a laser treatment system is disclosed as including a laser for providing a laser beam having a wavelength within a first predetermined range, at least one optical fiber having a first end in communication with the laser beam and a second end through which the laser beam is transmitted, a slug of fluorescent material positioned adjacent the second end of the optical fiber, a light source for providing an optical stimulus having a wavelength within a second predetermined range to the fluorescent slug, wherein a desired optical fluorescent response having a wavelength within a third predetermined range from the fluorescent slug is generated, a detector for detecting the optical fluorescent response, a device for receiving a first signal representative of the optical stimulus and a second signal representative of the optical fluorescent response, and a processor for determining a phase difference between the first and second signals, wherein the temperature of the optical fiber second end is determined as a function of the phase difference.
In accordance with a third aspect of the invention, an optical thermometry system is disclosed as including an optical fiber having a first end for receiving light and a second end for transmitting light, a slug of fluorescent material positioned adjacent the optical fiber second end, a light source for providing an optical stimulus through the optical fiber to the fluorescent slug in order to generate a desired optical fluorescent response therefrom, a detector for detecting the optical fluorescent response, a device for receiving a first signal representative of the optical stimulus and a second signal representative of the optical fluorescent response, and a processor to determine the phase difference between the first and second signals.
In accordance with a fourth aspect of the invention, a method of maintaining temperature of an optical fiber tip in a laser system within a specified range is disclosed as including the steps of positioning a slug of fluorescent material adjacent the optical fiber tip, providing an optical stimulus through at least one fiber optically linked to the optical fiber tip, wherein a desired optical fluorescent response from the fluorescent slug is generated, detecting a signal representative of the optical stimulus, detecting a signal representative of the optical fluorescent response, digitally processing the optical stimulus signal and the optical fluorescent response signal to determine a temperature for the optical fiber tip as a function of a phase difference therebetween, comparing the determined temperature for the optical fiber tip to the specified range, and modifying power output of the laser system as necessary to maintain temperature of the optical fiber tip within the specified range.
In accordance with a fifth aspect of the invention, a method of maintaining temperature of an optical fiber tip in a laser system at a desired temperature is disclosed as including the steps of processing specified light signals to determine a temperature for the optical fiber tip as a function thereof, comparing the determined temperature for the optical fiber tip to the desired temperature, generating an error signal as a function of any difference between the determined temperature and the desired temperature, and controlling power output to a laser diode of the laser system in accordance with the error signal.
In accordance with a sixth aspect of the invention, a system for maintaining temperature of an optical fiber tip in a laser system at a desired temperature is disclosed, wherein the laser system includes a laser diode for providing a laser beam to the optical fiber tip. The system includes a processor for determining a temperature for the optical fiber tip as a function of specified light signals detected in the laser system, a power amplifier for supplying power to the laserdiode, and a controller for providing a power output signal to the power amplifier, where the controller contains an algorithm for calculating the power output signal which is a function of an error signal generated by a comparison of the determined temperature and the desired temperature.